Process for the production of phosphorus and potash compounds



Patented May 6, 1924.

UNITED STATES PATENT OFFICE.

BETHUNE G. KLUGH, OF CHICAGO, ILLINOIS, ASSIGNOR TO FEDERAL PHOSPHOBUS v COMPANY, OF BIRMINGHAM, ALABAMA, A. CORPORATION OF ALABAMA.

PROCESS FOR THE PRODUCTION OF PHOSPHORUS AND POTASH COMPOUNDS. I

No Drawing. Application filed September 20,

To all whom. it may concern:

Be it known that I, BETHUNE G. KLUGH, a citizen of the United States of America, residing at Chicago, in the county of Cook E and State of Illinois, have invented certain new and useful Improvements in Processes for the Production of Phosphorus and Potash Compounds, of which the following is a specification. V

This invention relates to the electric smelting of a mixture of natural phosphate, potassium bearing silicate or aluminate rock and carbon to the end that the phosphorus and potash content of the charge will he simultaneously volatilized, the elemental phosphorus oxidized in the presence of the volatilized potash and the two constituents collected together as phosphoric acid and potash. a

My invention further contemplates the utilization, in processes for the electric smelting of phosphatic materials with or without iron, of potash bearing shale or silicate or aluminate rock to furnish the re uisite quantity of silica for the flux which as heretofore been supplied by sand or silicate rocks having no recoverable values.

My. invention further contem lates the production of a compound of p osphorus 3c and potash as a by-product of an electric furnace engaged in the production of commercial term-phosphorus, this being accomplish'ed by the charging of a potash bearing silicate instead of sand and the control of the temperature and stock depth in the furnace upon the principles defined in my pending application, Serial No. 388,822, filed June 14th, 1920.

I am aware that it has been proposed to 4c treat potassium bearing rocks, such as feldspar or muscovite, by heating them with natural phosphates, the principal constituent of which is tricalcium phosphate, preferably in an electric furnace and at temta peratures up to 2000 C. to produce potassium phosphate. These processes do not contemplate the admixture of carbon or ang other reducing agent with the charge an as described, are conducted with no reductc tionof the phosphorus. Such processes are based upon the assumption that the phosphorus passes out as phosphorus oxides and the potassium as potassium oxides or other volatile compounds thereof. Furthermore,-

1920, Serial No. 411,483. Renewed August 23. 1922. Serial No. 583,939.

these existing processes make no mention of any ratio of the silica and lime in the reactm mixture.

.l'y process hereindescribed difi'erentiates from such above described existing processes in that I have found that it is essential that the phosphorus must be reduced in order that itbe volatilized in commercial proportions and that the ratio of the silica and lime in the charge must be accurately pro ortioned in order that the quantity of phosp orus and potassium lost by passing out in the slag be kept within commercial limits.

To obtain the best operating results, my invention contemplates the treatment of the combined phosphorus and potash bearing elements and carbon in an electric furnace in accordance with the rinciples laid down in my pending app cation Serial No. 388,822, which require the correct porportioning of the carbon content of the charge, the avoidance of open arcs, the maintenance of uniform furnace temperatures preferably between 1200 and 1500 C. by the constant diffusion of the'electric heat through the slag bath, the preservation of a uniform depth of stock above the fusion zone, the automatic feed of the stock proportionate to the requirements of the fusion zone, and the preservation above the stock of a combustion space in which the evolved elemental phosphorus may be oxidized.

In addition to the foregoing I have found that special features are newssary for the cotemporaneous volatilization and collection of bothphosphorus and potash, whether or not in conjunction with the production of ferro-phosphorus. These are 1st: The flux, which should be acid to treat phosphatic materialand basic to treat potash materials, must be carefully calculated as to its proportions of lime and silica so that a minimum of phosphorus and potassium will be carried out of the furnace in the sle 2nd: ,Tlie phosphorus must be reduced then volatilized in the form of elemental hosphorus and subsequently oxidized to 0 with which volatillzed potassium combines to produce a compound of phosphoric acid and potashQhighly valuable for fertilizers and other uses.

1 will now describe my invention with special attention to all limitations of the various steps and features involved that are essential to its commercially and technically successful 0 eration, and in such conciseness that those s illed in the art may actually be enabled to successfully practice it.

In making up and proportioning my charge, I take a given quantity of any natural phosphate, consisting of the phosphorus bearing element, tricalcic phosphate, and I take into account the accompanying silica, alumina, iron oxide, and magnesia. I then take potassium bearing shale or other potassium bearing rock, and add it to the charge in such quantity that the total silica of the two above materials, of the molecular proportions corresponding to (CaO (81:0,) which corresponds to a uantitative ratio of 1.4 0:10 to 1.0 SiO I magnesia be present in the mixture in quantity greater than 5 per cent of the weight of the total silica and lime added together, it is calculated into the flux charge in the same molecular ratio as that of the0si)licahar;1d lime or dthat lqf lifgfl (Si 2 2 w ic correspon s to t e uantitative ratio of 1.0 part of MgO to 1.0 part of silica. The alumina present which usually is between 5' and 16 per cent of the total lime and silica together is in such case neglected in the flux calculation, because by actual practice I have found that the desired reactions and fluidity of the slag is little influenced by said alumina in said proportions.

The above described calculation of flux is not based upon any assumptions or chemical theories of what the behavior of such proportioned slags will be under the conditions prevailing in conducting the hereindescribed process but are the carefully noted results of actual practice in a commercial size unit of operation of said hereindescribed process over a period of sufficient time to prove beyond doubt the efiectiveness thereof. I have determined by said actual practice that, when smelting a charge in an electric furnace as in the hereindescribed process, the above described com osition of slag will be of the desired fiui ity for the successful operation of the electric furnace under essential conditions for carrying out the hereindescribed process, and that said slag will carry out of said furnace the minimum quantity of the phosphorus and potassium charged into and smelted in said furnace.

For the volatilization of phosphorus alone from natural phosphates and the practical elimination of phosphorus from the slag, there should be present in the charge in the smelting furnace, an excess of silica, over and above that required to combine with all the lime present in the ratio of (CaO) (SiO thus producing a so-called acid slag. On the other hand, to set free and volatilize potassium compounds from their associated rocks, there should be present an excess of lime over and above that required to combine with all the silica and alumina present in the total smelting charge, thus producing a so-called basic slag. Both theories of slag characteristics are correct for each above specific case, takensepa'rately, other conditions being properly provided. However, it is obvious that, when smelting the two above described materials for the purpose of jointly freeing and volatilizing both potassium and phosphorus compounds, it is impossible to have a slag both acid and basic i. e., with both an excess of lime and an excess of silica. But, regardless of assumptions or theories of the chemistry of the silicates and phosphates at high temperatures, which in the present state of the science is not explicative of phenomena occurring therein, I have discovered, practiced and proven that a lime, silica-alumina-magnesia ratio of the above described composition will, within the ratios and ranges specified fulfil the requirements for the successful conductance of the hereindescribed process.

To the charge of natural phosphate and shale or other natural potash bearing rocks, proportioned as above described I addcarbon preferably in the form of finely divided coke, in quantity necessary to reduce all of the phosphorus and iron in charge. This carbon calculation is based upon the hypothetical chemical equations:

I have found by actual commercial practice that, when less carbon is added than that required by the above e uations, a considerable portion of the p osphorus and even iron passes into the slag unreduced. Also when any appreciable excess of carbon above that required and calculated by the above equations is used in the charge, said carbon excess accumulates in the furnace, and causes great irregularity in fur nace operation, ,destroying possibility of electrical control, thuscausing overheating and contaminating fumes of SO and other constituents of the charge to be evolved, and defeating all other features of control of the process hereindescribed which make it a commercial operation.

With the above described furnace charge, I proceed with the operation by keeping the furnace charged continuously and uniformly over its entire surface of activity and maintaining the current flow entirely Within the slag, and avoiding open arcs which cause a volatilization of the various constituents of the charge such as iron, lime, silica, magnesia and alumina, which volatilized matcrials pass out of the furnace with the gases as fume and cause clogging of the gas mains and collecting equipment to such an extent as to reauire long interruptions of the operation an cleaning the entire gas system Furthermore, such volatilization of the above components of the stock disturb the balance in the proportion of the calculation of the reacting components, thus destroying a principal factor of control which determines the soccess of the operation.

I have further found by actual and accurate measurements that the temperature of the slag within the operating furnace hereindescribed must be maintained below 1450 C., and should preferably be between 1200 and 1350 C., and further that the temperature within the furnace must be grad'iently controlled so that each successive section of the stock within furnace, from the slag to the top of the charge is of a lower temperature than that section above which it lies. When the temperature within the furnace rises slag resultant of such increased temperature,

which produces arcing in the electric current flow, and intense heating of the charge by such superheating. In such state the slag will present no definite lane of contact for the tips of the electro es, thus producing violent surging of the flow of the current with arcing and breaking of the current, and creating irregular and heterogenous zones of excessive heating.

The accumulation of excessive carbon in the furnace from using an excess over that required for. combining with the oxygen in combination with the phosphorus and iron present in the charge and to form CO, will cause the formation of open arcs and overheating of the slag, producing the objectionable conditions'above described. Hence the importance of maintaining the carbon ratio as aforedescribed. By the oxygen in combination with the phosphorus and iron, I mean only the oxygen combined directly with the phosphorus or iron, as P 0 Fe O, Fe O Fe l) etc, and not that oxygen which exists in combinations with other bases, such as CaO, SiO etc., with which.

the respective phosphorus and iron oxides may be in further chemical combination.

On the other hand, Ihave found, by the maintaining of the regular and uniform charging of said furnace and further maintaining the temperature of the slag within said furnace between 1200 and 1350 C., that a regular and continuous flow of current will be maintained, and that the phosphoric acid, as oxidized from the elemental phosphorus evolved or the potassium so evolved will also be passed out of the'co'm-' layers of charge within the furnace from the slag upward is maintained the operation may proceed with uniformity, regularity, and continuity, and that the phosphoric acid oxidized from the elemental phosphorus evolved can be collected in a. very pure state and practically free from the contamination and interruption of operation by any accompanying fume and condensation product of silica, alumina, magnesia or constituents of the charge other than phosphorus or potassium compounds as desired.

I have further found and operated upon a commercial scale over a considerable period of modification of the principles of the aforedescribed process in the production of ferro-phosphorus, and have further found very distinct advantages to be gained thereby.

I take natural phosphate shale or other potassium bearing silicate rock, and carbon, in the proportions aforedescribed, 1 then add iron in proportion to the phosphorus to produce the desired ferro-phosphorus. I have further found that in the production of ferro-phosphorus, by this means, a portion of the phosphorus is always volatilized. The proportion of the tOtElPhOSPhOIllS volatilized is dependent upon the quantity and physical state of,the iron present with the charge to absorb the phosphorus as reduced. For instance, if enough iron is present in the charge so that an alloy containing eighteen per cent phosphorus is produced, there will be about ten per cent of the total phosphorus volatilized; and if enough iron is present in the charge so that an alloy containing twenty per cent phosphorus is produced, there will be about fifty per cent of the total phosphorus volatilized. The above figures will vary somewhat depending upon the physical condition of the charge and certain inherent characteristics of the individual furnace construction and operation, But for any given lot of commercially availableraw materials and any individual. furnace, this lowering temperatures of the successive determine factor of (phosphorus volatilization may be charge of natural phosphate, potash bearing silicate rock and carbon, I can by experiment determine, how much of the phosphorus contained in the charge will be absorbed bv agivcn quantity of iron added to the charge and how much will be volatilized. I

' a definite chemical compound of potassium hosphate. In this way this rocess may he used for the production of a efinite compound of potassium phosphate.

It is evldent that in commercially available raw materials, the natural phosphates will contain varying proportions of phoshorus, silica, and lime, and the otassium hearing shales or other rock wil contain varying proportions of potassium, silica, alumina and lime. Commercially available carbon reducing agent materials will also con tain varying proportions of, silica, alumina, lime and magnesia. Therefore with the number of variables effecting the above operation, it is self evident that a coincidence of proportions of contents of the governing constituents, so that, the ratio of the silica and lime will be in the ratios aforedescribed, and also the ratio of the potassium and phosphorus in the proportions that exist in potassium phosphate, is not commercially possible. However with my process, iron, by proportioning the commercially available natural phosphate and potassium bearing silicate rock so as to roduce the requisite character of slag, and by addin to this charge, including the reducing car on, sufficient iron to absorb a portion of the phosphorus, which I will top out of the furnace as ferro-phosphorus, volatilize and oxidize the rema ning phosphorus in predetermined proportion necessary to roduce, with the potassium volatilized,a de nite compound of potassium phosphate. At the same time in controlling the phosphorus volatilized by absorbing said predetermined portion with iron in the smelting charge, I will have produced a commercial product, and may make either the ferro-phosphorus or the potassium phosphate the principal product.

In case I produce ferro-phosphorus by the aforedescribed process, I may consider in its commercial aspect that the potassium bearing shale is added in lieu of the silicious flux to the natural phosphate, in which case, with the properly proportioned charge as afore- Now by taking any givenacaaria described, the potassium will be volatilized and collected along with the phosphorus oxides, which will considerably lower the cost of ferro-phosphorus production.

Furthermore in either case of the production of potassium phosphate or otash and phosphoric acid mixtures, or of erro-phosphorus, and the collection of the otash and phosphoric acid, the collection 0 the phosphorlc acid is greatly facilitated by the presence of the potash.

The phosphoric acid and potash may be separated from the accompanying gases by any of several methods such as electrical recipitation, absorption towers, or, since t ere will usually be an excess of phosphoric acid with the potash, ammonia gases may be passed into the potash and phosphoric acid earing gases after withdrawin them from the furnace, thus combining t e ammonia with the phosphoric acid and producing a complete fertllizer containing chemically com ined ammonium potassium hosphate, in a dry powder direct and ready for distribution and use.

Having thus described my invention; what I claim as new and desire to secure by Let ters Patent, is

1. The hereindescribed process, which consists in smelting in an electric furnace phosphate and potash bearing materials, with carbon in approximately the ratio required to combine with the oxygen combined in the charge with the phosphorus and iron present to form 00, oxidizing the evolved elemental phosphorus, causing the resultant phosphoric acid to combine with the evolved potash, and recovering the resultant compound of phosphorus and potash.

2. The process according to claim 1, in which the reduction is conducted attemperatures ranging from 1200 C. to 1500 (1., and in the absence of open arcs.

3. The process according to claim 2, in which the stock depth above the fusion zone is maintained substantially constant and of adually decreasing temperature upwardly rom the fusion zone.

4. The process according to claim 1, in which the phosphorus is evolved as elemental phosphorus and oxidized in the presence of the volatilized potash, which combines therewith to form a compound of potash and phosphorus.

5. The hereindescribed process for the recovery of compounds of phosphorus and otash, which consists in charging potash caring shale with phosphatic material and a carbon reducing agent in ratio required for direct reduction of P 0 in said phosphatie materials in an electric furnace, smelting the mixture, oxidizing the volatilized phosphorus in the presence of the volat-ilized potash, and recovering the com pound of potash and phosphorus.

6. The process according to claim 5, in which the total lime and silica in the charge shall be in the approximate molecular ratio of (CaO) to (810 7 e process according to claim 5, in which the flux shall comprise silicaand lime in the ratio of 1.4 parts of lime to 1.0 of silica 8. The process according to claim 7, in which magnesia in excess of 5 per cent is calculated into the flux charge in the same ratio as silica.

9. The hereindescribed process for the joint production of ferro-phosphorus and compounds of phosphorus and potash, which consistsin smelting in an electric furnace phosphatic material and iron with only sufficient carbon to reduce the iron and liberate the phosphorus, and with a silicious flux in the form of a potash bearing silicate.

10. The process according to claim 9, in

i which potash bearing shale is used as the source of silicious flux and its quantity is proportioned toproduce a flux containing substantially 1.4 parts of silica to 1.0 parts of lime. f

11. The hereindescribed process for producing potassium-phosphate, which consists in charginga smelting furnace with phosphate and potash bearing materials and a reducing agent, and adding iron suflicient to absorb the charge in excess of that required to comphosphorus content of thebine with the content of the charge.

phorus and potash are combined as the evolved phosphorus is oxidized, and recovered as potassium'phosphate.

' 13. The hereindcscribed process. for the 7 production ammonium potassium phosphate which consists in smelting phosphate andpotash bearing materials in the presence of carbon in an electric furnace, oxidizing the evolved elemental phosphorus to form P 0 combining the volatilized potash with the P 0 combining ammonia with the free phosphoric acid, and recovering ammonium potassium phosphate.

14. The process according to claim 13, in which theconstituents of the charge are proportioned to give an-excess of P 0 gases above that needed to form potassium phosphate, and this excess of phosphoric acid is used to fix the ammonia in ammonia gas added to the mixture of P 0 and potassium" phosphate to form as a resultant product ammonium potassium Fhosphate.

In testimony whereo I afiix my signature.

Witness:

Nom WELBH. 

